The broad objective of this project is to advance the knowledge of fundamental processes involved in sequential anaerobic and aerobic PCB degradation. This interdisciplinary research should yield biotechnology that is based on sequential anaerobic-aerobic degradation and results in mineralization of a wide range of PCBs and therefore will reduce biological activities and toxicity of one of the most ubiquitous and troublesome cases of Superfund chemicals. Specific aims of the proposed research are: (I) evaluation of the effect of FeSO4 on and enhancement of dechlorination of Aroclors and sediment associated PCBs by mixed cultures and enrichments of dechlorination of Aroclors and sediment associated PCBs by mixed cultures and enrichments; (II) evaluation of metabolic of metabolic rate and toxicity of PCB intermediates; (III) enhancement of recombinant degradative pathways for ortho-substituted PCBs; and (IV) elucidation of the composition and dynamics of mixed microbial populations involved in PCB degradation and manage combinations of populations for enhanced bioremediation. The proposed work builds on our recent discoveries that FeSO4 stimulates anaerobic dechlorination of Aroclor and that a single-step upgrading of pre-existing pathways with aromatic dechlorinases yields bacteria that now grow on some of the products of anaerobic PCB dechlorination. The stimulatory effect of FeSO4 will be further studied on (i) a wider combination of Aroclors and inocula, (ii) in situ dechlorination of field weathered PCBs in sediments, and (iii) the major individual dechlorination processes known to occur in situ. These efforts will enable production of more completely dechlorinated PCB mixtures with increased susceptibility to aerobic metabolism. To develop these aerobic phase of PCB bioremediation, recently engineered recombinant PCB pathways will be further enhanced to minimize accumulation of toxic intermediates and for better coordination of participating pathways. This should yield bacteria with improved growth on a wider array of anaerobically produced PCBs. A comprehensive study of diversity, dynamics and metabolic shifts within PCB degrading mixed communities will provide knowledge needed to advance further understanding of the molecular, population and environmental factors that control the environmental fate of PCBs in Superfund sites.